This application relates to mobile air compressors. Specifically, the application relates to systems for protecting air compressor motors from stalling and burnout under conditions in which the electric power supplied to an air compressor motor may fall below a rated or operational level.
Mobile air compressors are known in the building industry. Such compressors typically comprise an air intake protected by a filter. Air taken into the intake is passed down an airline to a cylinder with an oscillating piston which compresses the air, after which the compressed air is then passed down a further airline to a storage tank, or compressor tank. The cylinder, or compression means, is driven by a motor which is typically designed to operate at a rated voltage to conform with the potential difference which is typically available domestically. In the USA this is about 120 volts, but it differs from country to country. Air flow from the compressor tank passes along a final airline to quick connect coupler outlets, which in turn may be coupled to be operable with a variety of tools known in the art. The passage of air between the compressor tank and the chosen tool is regulated by a control knob which lies in the final line.
However, problems in the art beset users of air compressors. One problem arises when the compressor draws its electrical power from a cable that may be longer than 20 feet, sometimes even up to 100 feet. This situation frequently arises when a portable compressor is used on a building site. The power outlet is typically located at a fixed point on the site, but the compressor may be required at a location remote from the outlet. However, the impedance of a long power cable may be relatively high, and consequently may have the result that the voltage, or potential difference, available to the compressor is diminished and is not the same as the voltage available at the power outlet. Accordingly, it is also not the same as the rated voltage under which the motor is designed to operate. This tends to have the undesirable result that the motor tends to stall during operation. Being an induction motor, rather than slowing down it continues at about the same speed as under the design or rated voltage, but tends to lose torque output and then to simply stall where the torque load is greater than the motor's torque output.
The same problem may arise due to different causes. For example it is found that cold weather may affect the voltage output at the end of an electric current cable, or it may reduce the torque deliverable by the motor.
This can be an exasperating experience to an operator, and there is presently no simple solution to this problem. As a result, expensive compressors may be found to be quite useless under certain conditions that arise fairly frequently.
Thus there is a need in the art for a compressor that addresses problems in the art. The present invention addresses these and other needs.